Chromeless phase-shifting mask for equal line/space dense line patterns

ABSTRACT

A phase-shifting mask suited for equal line/space, small pitched, dense line pattern is disclosed. The phase-shifting mask includes a transparent substrate, a partially shielded mesa line pattern of first phase formed on the substrate, and a clear recessed line pattern of second phase etched into the substrate and is disposed right next to the partially shielded mesa line pattern. The partially shielded mesa line pattern has a plurality of alternating 5%-10% transmittance light-shielding regions and clear regions of the first phase. The partially shielded mesa line pattern and the clear recessed line pattern have the same line width. The light that passes through the clear regions of the first phase and the light that passes through the clear recessed line pattern of second phase have a phase difference of 180 degree.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a phase-shifting mask (PSM), and moreparticularly, to a chromeless PSM for equal line/space dense linepatterns and lithographic method of employing such chromeless PSM.

2. Description of the Prior Art

Lithography processing, which is an essential technology whenmanufacturing conventional integrated circuits, is used for defininggeometries, features, lines, or shapes onto a die or wafer. In theintegrated circuit making processes, lithography plays an important rolein limiting feature size. By using lithography, a circuit pattern can beprecisely transferred onto a die or wafer. Typically, to implement thelithography, a designed pattern such as a circuit layout pattern or anion doping layout pattern in accordance with a predetermined design ruleis created on one or several mask in advance. The pattern on the mask isthen transferred by light exposure, with a stepper and scanner, onto thewafer.

It is critical in this field to solve resolution of the lithographicprocess as the device sizes of the semiconductor industry continue toshrink to the deep sub-micron scale. There are primarily two methods inthe prior art for improving resolution. One method involves using shortwavelengths of light to expose a photoresist layer on the semiconductorwafer. Short wavelengths of light are desirable as the shorter thewavelength, the higher the possible resolution of the pattern. Anothermethod involves the use of a phase-shifting mask (PSM) to improve theresolution of the pattern transferred to the semiconductor wafer.

Please refer to FIG. 1, which is a structural diagram of a prior artalternating phase-shifting mask 10. As shown in FIG. 1, a fully opaquematerial such as chrome is used in a non-transparent region 12 of thealternating phase-shifting mask 10, and the non-transparent region 12 isflanked by transparent regions 14, 16. Both of the transparent regions14, 16 are made of quartz. The thickness of the transparent region 14 isless than that of the transparent region 16. Therefore, light thatpasses through the transparent region 14 has a 180-degree phase shiftrelative to light that passes through the thicker transparent region 16,which results in destructive interference and image contrast.Consequently, during the lithographic process, a dark unexposed regionfalls on an area of a photoresist layer and is located below thenon-transparent region 12 of the alternating phase-shifting mask 10.

However, the alternating phase-shifting mask (alt-PSM) 10 has to performa double-exposure/two-mask lithography process involving a trim mask tocomplete pattern transferring. The first mask is a phase-shifting maskand the second mask is a single-phase trim mask. The phase-shifting maskprimarily defines regions requiring phase shifting. The single-phasetrim mask primarily defines regions not requiring phase shifting.However, this optical proximity correction (OPC) technique suffers fromtransmission imbalance occurred in phase shifted and non-phase-shiftedregions and other flaws caused by alt-PSM.

Therefore, a chromeless phase-shifting mask is developed. Please referto FIG. 2, which is a structural diagram of a prior art chromelessphase-shifting mask 20. As shown in FIG. 2, the chromelessphase-shifting mask comprises a transparent region 22 made of quartz,and the transparent region 22 is flanked by two transparent regions 24,26 also made of quartz. The transparent region 22 is thicker than boththe transparent regions 24, 26, which causes a 180 degree phase-shiftingin light passing through the transparent regions 24, 26.

In other words, the transparent regions 24, 26 are phase-shiftingregions, and the transparent region 22 is a non-phase-shifting region.Because of this 180-degree phase difference, there is destructiveinterference at the phase boundaries of the phase-shifting regions 24,26 and the non-phase-shifting region 22. Consequently, during thelithographic process, a dark unexposed region falls on an area of aphotoresist layer and is located below the non-phase-shifting region 22of the chromeless phase-shifting mask 20.

However, with the increase of packing density of devices such as dynamicrandom access memory (DRAM) devices, a pitch between adjacent microfeatures of the device such as word line pitch shrinks dramatically.Please refer to FIG. 3. FIG. 3 is a plan view of a portion of word lines32 overlying a semiconductor wafer 30. As shown in FIG. 3, pitch P ofthe word lines 32 is equal to the combination of line width L and thespacing S between two adjacent word lines 32 (P=L+S). When the linewidth L is less than or equal to 100 nm, and the pitch P issubstantially equal to the twice of the line width L of the device andforms a dense pattern, light of 0 degree phase-shifting and light of 180degrees phase-shifting cancel out. Therefore, the prior art chromelessphase-shifting mask fails to transfer the dense pattern.

SUMMARY OF INVENTION

It is therefore an object of the claimed invention to provide achromeless phase-shifting mask for solving the above-mentioned problems.

According to the claimed invention, a chromeless PSM for forming equalline/space, small pitched, dense line pattern is disclosed. Thechromeless PSM includes a transparent substrate, a partially shieldedmesa line pattern of first phase formed on the substrate, and a clearrecessed line pattern of second phase etched into the substrate and isdisposed right next to the partially shielded mesa line pattern. Thepartially shielded mesa line pattern has a plurality of alternating5%-10% transmittance light-shielding regions and clear regions of thefirst phase. The partially shielded mesa line pattern and the clearrecessed line pattern have the same line width. The light that passesthrough the clear regions of the first phase and the light that passesthrough the clear recessed line pattern of second phase have a phasedifference of 180 degree.

From one aspect of this invention, a chromeless PSM comprises atransparent substrate; a plurality of first phase-shifting line patternshaving a first substrate thickness of first phase disposed on thetransparent substrate along a first direction, wherein each of the firstphase-shifting line patterns is disposed thereon clear regions of thefirst phase and 5%-10% light transmittable block areas. A plurality of100% light transmittable second phase-shifting line patterns, inparallel with the first phase-shifting line patterns, has a secondsubstrate thickness of second phase. The first phase-shifting linepatterns and second phase-shifting line patterns have the same linewidth and are alternately disposed on the transparent substrate.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings:

FIG. 1 is a structural diagram of a prior art alternating phase mask;

FIG. 2 is a structural diagram of a prior art chromeless phase-shiftingmask;

FIG. 3 is a plan view of a portion of word lines overlying asemiconductor wafer;

FIG. 4 is a plan view of a portion of the layout of a chromeless PSM inaccordance with one preferred embodiment of this invention;

FIG. 5 is a schematic, cross-sectional view of the chromeless PSM takenalong line I-I of FIG. 4;

FIG. 6 is a schematic, cross-sectional view of the chromeless PSM takenalong line II-II of FIG. 4;

FIG. 7 is a plan view of a portion of the resultant equal line/spacedense line pattern transferred from the chromeless PSM of this inventionto a photoresist film coated on a wafer;

FIG. 8 is a schematic diagram illustrating the CD uniformity of theequal line/space dense line patterns 202 a and 202 b of FIG. 7 accordingto the first preferred embodiment of this invention;

FIG. 9 is a plan view of a portion of the layout of a chromeless PSM inaccordance with second preferred embodiment of this invention;

FIG. 10 is a schematic, cross-sectional view of the chromeless PSM takenalong line I-I of FIG. 9;

FIG. 11 is a schematic, cross-sectional view of the chromeless PSM takenalong line II-II of FIG. 9;

FIG. 12 is a plan view of a portion of the resultant equal line/spacedense line pattern transferred from the chromeless PSM of FIG. 9 to aphotoresist film in accordance with the second embodiment of thisinvention; and

FIG. 13 is a schematic diagram illustrating the CD uniformity of theequal line/space dense line patterns 202 a and 202 b of FIG. 12according to the second preferred embodiment of this invention.

DETAILED DESCRIPTION

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 4-13 of the drawings, whereinlike numerals designate like components, areas or regions. Features ofthe invention are not drawn to scale in the drawings.

The present invention pertains to an improved chromeless phase-shiftingmask (PSM), which is capable of solving equal line/space, small pitched,dense line patterns such as word lines or gate conductors oftrench-capacitor dynamic random access memory (DRAM) devices havingcritical line width that is less than or equal to 100 nanometers. Thecritical dimension (CD) uniformity of the resultant equal line/spacedense line pattern transferred from the chromeless PSM of this inventionto a photoresist film coated on a wafer is also enhanced.

Please refer to FIGS. 4-7, wherein FIG. 4 is a plan view of a portion ofthe layout of a chromeless PSM in accordance with one preferredembodiment of this invention; FIG. 5 is a schematic, cross-sectionalview of the chromeless PSM taken along line I-I of FIG. 4; FIG. 6 is aschematic, cross-sectional view of the chromeless PSM taken along lineII-II of FIG. 4; FIG. 7 is a plan view of a portion of the resultantequal line/space dense line pattern transferred from the chromeless PSMof this invention to a photoresist film coated on a wafer.

As shown in FIG. 4, the chromeless PSM in accordance with one preferredembodiment of this invention comprises a transparent quartz substrate100, a plurality of first phase-shifting line patterns 102 a-102 farranged in parallel with each other along the reference Y-axis, and aplurality of second phase-shifting line patterns 104 a-104 e arranged inparallel with each other along the reference Y-axis. According to thepreferred embodiment, the line width of each of the first phase-shiftingline patterns 102 a-102 f and the line width of each of the secondphase-shifting line patterns 104 a-104 e are the same.

The aforesaid first phase-shifting line patterns 102 a-102 f and secondphase-shifting line patterns 104 a-104 e are alternately formed on thequartz substrate 100. By way of example, the second phase-shifting linepattern 104 a is disposed between the first phase-shifting line pattern102 a and the first phase-shifting line pattern 102 b, the secondphase-shifting line pattern 104 b is disposed between the firstphase-shifting line pattern 102 b and the first phase-shifting linepattern 102 c, and so forth. Besides, along each of the firstphase-shifting line patterns 102 a-102 f, a plurality of block areas 106a-106 f are provided. The block areas are disposed spaced apart fromeach other along each of first phase-shifting line patterns 102 a-102 f.As shown in FIG. 4, for example, a 100%-light transmission firstphase-shifting area 108 a is disposed between two adjacent block areas106 a along the first phase-shifting line pattern 102 a. The block areasare equal in size and have a light transmission rate of about 5%-10%,i.e., merely 5%-10% of the incident light can pass through each of theblock areas.

According to the first preferred embodiment, each of the block areas 106a-106 f is masked by a phase shifter such as MoSi, MoSiO, MoSiON or thelike.

Therefore, the second phase-shifting line patterns 104 a-104 e of thechromeless PSM of this invention are 100% light transmittable. Each ofthe first phase-shifting line patterns 102 a-102 f of the chromeless PSMencompasses alternating 100% light transmittable clear areas and 5%-10%light transmittable block areas. The phase-shifting mask of thisinvention is partially shielded along the mesa line pattern 102 a-102 fof first phase. According to the first preferred embodiment, the lengthof one side of each of the rectangular 5%-10% light transmittable blockareas 106 a-106 f along the reference Y-axis ranges approximately fromλ/4 to 3λ/4 (λ: wavelength of the exposure light source of the stepperand scanner, in nanometer). The length of one side of each of therectangular 100% light transmittable clear areas 108 a-108 f along thereference Y-axis ranges approximately from λ/4 to 3λ/4.

As shown in FIG. 5 and FIG. 6, the thickness of the quartz substrate 100underneath each of the first phase-shifting line patterns 102 a-102 f isdenoted as t₁, and the thickness of the quartz substrate 100 underneatheach of the second phase-shifting line patterns (also referred to as“clear recessed line patterns”) 104 a-104 e is denoted as t₂, whereint₁is greater than t₂(t₁>t₂), such that light passing through the quartzsubstrate 100 having different thicknesses produces image contrast. Thephase difference between the phase of light passed through the firstphase-shifting line patterns 102 a-102 f and the phase of light passedthrough the second phase-shifting line patterns 104 a-104 e is 180degree. Preferably, the phase of light passed through the firstphase-shifting line patterns 102 a-102 f is 0-degree, while the phase oflight passed through the second phase-shifting line patterns 104 a-104 eis 180-degree (π).

According to the first preferred embodiment, the plurality of spacedapart 5%-10% light transmittable block areas 106 a-106 f, which aredisposed on each of the first phase-shifting line patterns 102 a-102 f,are aligned with the reference X-axis. By providing such unique layoutof the chromeless PSM, resultant dense line patterns 202 a-202 ftransferred from the chromeless PSM of this invention to a photoresistfilm coated on a wafer is depicted in FIG. 7. However, the criticaldimension (CD) uniformity of the resultant dense line pattern (in equalline/space fashion) is still not satisfactory.

Please refer to FIG. 8. FIG. 8 is a schematic diagram illustrating theCD uniformity of the equal line/space dense line patterns 202 a and 202b of FIG. 7 according to the first preferred embodiment of thisinvention. As can be seen in this figure, the variation of the CD of theline pattern 202 a or 202 b is high, and leads to wavelike lineprofiles.

Please refer to FIGS. 9-12, wherein FIG. 9 is a plan view of a portionof the layout of a chromeless PSM in accordance with second preferredembodiment of this invention; FIG. 10 is a schematic, cross-sectionalview of the chromeless PSM taken along line I-I of FIG. 9; FIG. 11 is aschematic, cross-sectional view of the chromeless PSM taken along lineII-II of FIG. 9; FIG. 12 is a plan view of a portion of the resultantequal line/space dense line pattern transferred from the chromeless PSMof FIG. 9 to a photoresist film in accordance with the second embodimentof this invention.

As shown in FIG. 9, the chromeless PSM in accordance with the secondpreferred embodiment of this invention comprises a transparent quartzsubstrate 100, a plurality of first phase-shifting line patterns 102a-102 f arranged in parallel with each other along the reference Y-axis,and a plurality of second phase-shifting line patterns 104 a-104 earranged in parallel with each other along the reference Y-axis.According to the second preferred embodiment, the line width of each ofthe first phase-shifting line patterns 102 a-102 f and the line width ofeach of the second phase-shifting line patterns 104 a-104 e are thesame.

Likewise, the aforesaid first phase-shifting line patterns 102 a-102 fand second phase-shifting line patterns 104 a-104 e are alternatelyformed on the quartz substrate 100. By way of example, the secondphase-shifting line pattern 104 a is disposed between the firstphase-shifting line pattern 102 a and the first phase-shifting linepattern 102 b, the second phase-shifting line pattern 104 b is disposedbetween the first phase-shifting line pattern 102 b and the firstphase-shifting line pattern 102 c, and so forth. Besides, along each ofthe first phase-shifting line patterns 102 a-102 f, a plurality of blockareas 106 a-106 f are provided. The block areas are disposed equallyspaced apart from each other along each of first phase-shifting linepatterns 102 a-102 f. As shown in FIG. 9, for example, a 100%-lighttransmission first phase-shifting area 108 a is disposed between twoadjacent block areas 106 a along the first phase-shifting line pattern102 a. These block areas are equal in size and have a light transmissionrate of about 5%-10%, i.e., merely 5%-10% of the incident light can passthrough each of the block areas.

Therefore, the second phase-shifting line patterns 104 a-104 e of thechromeless PSM of this invention are 100% light transmittable. Each ofthe first phase-shifting line patterns 102 a-102 f of the chromeless PSMencompasses alternating 100% light transmittable clear areas and 5%-10%light transmittable block areas. According to the second preferredembodiment, the length of one side of each of the rectangular 5%-10%light transmittable block areas 106 a-106 f along the reference Y-axisranges approximately from λ/4 to 3λ/4 (λ: wavelength of the exposurelight source of the stepper and scanner in nanometer). The length of oneside of each of the rectangular 100% light transmittable clear areas 108a-108 f along the reference Y-axis ranges approximately from λ/4 to3λ/4. Each of the block areas 106 a-106 f may be formed from phaseshifter such as MoSi, MoSiO, MoSiON or the like.

As shown in FIG. 10 and FIG. 11, the thickness of the quartz substrate100 underneath each of the first phase-shifting line patterns 102 a-102f is denoted as t₁, and the thickness of the quartz substrate 100underneath each of the second phase-shifting line patterns 104 a-104 eis denoted as t₂, wherein t₁ is greater than t₂ (t₁>t₂), such that lightpassing through the quartz substrate 100 having different thicknessesproduces image contrast. The phase difference between the phase of lightpassed through the first phase-shifting line patterns 102 a-102 f andthe phase of light passed through the second phase-shifting linepatterns 104 a-104 e is 180 degree. Preferably, the phase of lightpassed through the first phase-shifting line patterns 102 a-102 f is0-degree, while the phase of light passed through the secondphase-shifting line patterns 104 a-104 e is 180-degree (π).

According to the second preferred embodiment, the 5%-10% lighttransmittable block areas on two adjacent first phase-shifting linepatterns are not aligned with the reference X-axis. For example, as bestseen in FIG. 9, the spaced apart 5%-10% light transmittable block areas106 a, 106 c, and 106 e, which are disposed on each of the firstphase-shifting line patterns 102 a, 102 c, and 102 e, respectively, arealigned with the reference X-axis, while the spaced apart 5%-10% lighttransmittable block areas 106 b, 106 d, and 106 f, which are disposed oneach of the first phase-shifting line patterns 102 b, 102 d, and 102 f,respectively, are aligned with the reference X-axis. By providing suchimproved layout of the chromeless PSM, resultant dense line patterns 302a-302 f transferred from the chromeless PSM of this invention to aphotoresist film coated on a wafer is depicted in FIG. 12. The CDuniformity of the resultant dense line pattern (in equal line/spacefashion) is enhanced.

FIG. 13 is a schematic diagram illustrating the CD uniformity of theequal line/space dense line patterns 202 a and 202 b of FIG. 12according to the second preferred embodiment of this invention. As canbe seen in this figure, the variation of the CD of the line pattern 302a or 302 b is reduced.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A phase-shifting mask (PSM), comprising: a transparent substrate; afirst phase-shifting line pattern having multiple first columns, eachfirst column having first transparent regions and first 5%-10% lighttransmittable block areas intermittently and alternately disposed withrespect to the first transparent regions on the transparent substratealong a first direction and multiple second columns respectively havingsecond transparent regions each aligning a corresponding one of thefirst 5%-10% light transmittable block areas and second 5%-10% lighttransmittable block areas intermittently and alternately disposed withrespect to the second transparent regions on the transparent substratealong the first direction, wherein each second 5%-10% lighttransmittable block area aligns a corresponding one of the firsttransparent regions in a second direction; and a 100% lighttransmittable second phase-shifting line pattern having multiple columnseach sandwiched between two adjacent first column and second column ofthe first phase-shifting line pattern.
 2. The PSM of claim 1 wherein the5%-10% light transmittable block areas are equal in size.
 3. The PSM ofclaim 1 wherein the 5%-10% light transmittable block areas are disposedequally spaced apart along each of the first phase-shifting linepatterns.
 4. The PSM of claim 1 wherein the 5%-10% light transmittableblock areas on odd columns of the first phase-shifting line patterns arealigned with a second direction normal to the first direction, while the5%-10% light transmittable block areas on even columns of the firstphase-shifting line patterns are aligned with the second direction. 5.The PSM of claim 1 wherein each of the 5%-10% light transmittable blockareas has a length along the first direction ranging from λ/4 to 3λ/4(λ: wavelength of exposure light source of a stepper and scanner). 6.The PSM of claim 1 wherein each of the first and second transparentregions has a length along the first direction ranging from λ/4 to 3λ/4(λ: wavelength of exposure light source of a stepper and scanner). 7.The PSM of claim 1 wherein the first phase-shifting line pattern has afirst substrate thickness and the 100% light transmittable secondphase-shifting line pattern has a second substrate thickness, andwherein the first substrate thickness is greater than the secondsubstrate thickness such that light that passes through the first andsecond transparent regions and light that passes through the 100% lighttransmittable second phase-shifting line pattern have a phase differenceof 180 degree.
 8. The PSM of claim 1 wherein the transparent substrateis a quartz substrate.
 9. The PSM of claim 1 wherein the 5%-10% lighttransmittable block areas comprise phase shifter.
 10. The PSM of claim 9wherein the phase shifter comprises MoSi, MoSiO or MoSiON.
 11. Aphase-shifting mask (PSM), comprising: a transparent substrate; a firstpartial light transmittable pattern formed on the transparent substrate;a second transparent pattern having a height lower than that of thefirst partial light transmittable pattern formed on the transparentsubstrate; and a third transparent pattern having a height lower thanthat of the second transparent pattern defined between the first partiallight transmittable pattern and the second transparent pattern.
 12. ThePSM of claim 11 wherein the first partial light transmittable patternhas a length along a first direction ranging from λ/4 to 3λ/4 (λ:wavelength of exposure light source of a stepper and scanner).
 13. ThePSM of claim 12 wherein the second transparent pattern has a lengthalong the first direction ranging from λ/4 to 3λ/4 (λ: wavelength ofexposure light source of a stepper and scanner).
 14. The PSM of claim 11wherein the second transparent pattern has a first substrate thicknessand the third transparent pattern has a second substrate thickness, andwherein the first substrate thickness is greater than the secondsubstrate thickness such that light that passes through the secondtransparent pattern and light that passes through the third transparentpattern have a phase difference of 180 degree.
 15. The PSM of claim 11wherein the transparent substrate is a quartz substrate.
 16. The PSM ofclaim 11 wherein the first partial light transmittable pattern comprisesphase shifter.
 17. The PSM of claim 16 wherein the phase shiftercomprises MoSi, MoSiO or MoSiON.